Multiplex communication system



Oct. 17, 1933. F. scHRbTER'Er AL MULTIPLEX COMMUNICATION SYSTEM Filed00$. 18, 1930 INVENTORS FRITZ SCHROTER WALDEMAR ILBERG ATTORNEY reameca. 17, 1933 MULTIPLEX COIEMUNICATION SYSTEM Fritz Schrtiter andWaldemar Ilberg, Berlin, Germany, assignors to Telefunken Gesellschaftfur Drahtlose Telegraphic m. b. 11., Berlin, Germany, a corporation ofGermany Application October 18,

and in Germany October '19, 1929 6 Claims.

Owing to the increasingly greater lack of wavelengths due to the growingnumber of radiotelegraphic lines or channels there has arisen a need fora method and means whereby it is possible to operate two or moresuchlines or channels upon one and the same carrier wave without any mutualinterference or disturbance between signals being caused.

- This is accomplished in the present inventionby insuring that thetransmitters working on the same wave on the several channels neverradiate waves simultaneously. In accordance with this invention thesignals are emitted from thetransmitters alternately at more or lessshort l5 time intervals. At the same rhythm or cycle,

the several receivers corresponding to the channels operated on the"same wave-length are switched in successively so that at any giveninstant only that particular receiver apparatus will 50 be operativewhose respective transmitter is at the time sending out signals.

The invention has been illustrated in one of its preferred forms by theaccompanying drawing,

wherein: Q5 Fig. 1 explains the underlying principle schematically foran arrangement wherein three lines are to be operated simultaneously,and Fig. 2 illustrates a preferredform of receiver device for receivingthe signals transmitted. 3T9 Now referring to the drawing and first tothe transmitter of Fig. 1, consecutive connection of the threetransmitters is here accomplished by revolving switches a1, a2, a:respectively. The contact arms or wipers of these switches are driven bysuitable mechanism in synchronism and under co -phasic conditions. Threesimilar switching devices are provided in the receivers adapted toreceive signals from the respective transmitters. These switches aredesignated by letters b1, b2, b3, and they rotate in synchronismin-relation to one another and with the corresponding transmitterswitches. In the drawing it has been supposed that these receiverswitches cause rhythmically separationpr breaking of the connectionbetween the output circuit of the radio receivers and the indicators ordetector devices. These indicators may be ink recording devices asshown. It will be understood that the switch device may be interposed atany other suitable place in the receiver.

The number of switching cycles per second may be so chosen that the timerequired for a given cycle to elapse will be less than the briefesttelegraphic impulse to be transmitted, in other 1930, Serial No.489,512,

words, less than a dot in the case of the Morsecode. I

It will then not be necessary to take into consideration at all thequestionoi the position at any time of the synchronous switch whetherthe signals are sent off by hand or from an automatic or machinetransmitter. v So far as the receiving end is concerned, it may then beof advantage to storeup the signal beyond the length or duration of aswitch cycle in order that the action upon the indicator, such as theink recorder, of the receiver owing to the division of the signal by thechange-over switch of thereceiver may be rendered'harmless. A-practical. example of a scheme of signal accumulation 'comprising theuse of a glow-discharge or gaseousconduction-lamp is shown in Fig. 2.The indicator means 8 of the receiver outfit being of the inking kind inthis case is here associated by way of main electrodes 9 and 10 forming.a dischargegap 6 with a source of current 7 furnishing a potentialranging between the striking and extinguishing voltage of. theglow-discharge gap so that by itself it will be unable to result ininitiation of the glow-discharge. The incoming signal impulses arecaused to result in flashing of the glow-discharge gap by way of thesegment '4 of the synchronous switch (which in the case of threeconnections on the same wave-length as here concerned amounts to360:3=l20) by causing the incoming alternating current potential,

if desired, after'rectification, to act between one electrode 10 and anauxiliary electrode 11 of the glow-discharge gap. After completion of aswitching cycle, the glow-discharge current feeding the receiverindicator and released by the. auxiliary ignition potential supplied bythe receiver is broken each time by conducting the said glow-dischargecurrent through a second segment 5 of the synchronous switch whichcomprises almost a complete circle but which has the non-conductingsegment 57 interrupting the com- I plete circular conducting path 5.Thus, the voltage of the battery 7 is removed fromacross the tubeelectrodes 9 and 10 each time the distributor brush contacts with thesection or segment 5' oi. the ring 5. When the battery voltage is againapplied across the tube 6 by a further rotation of the distributor theincoming signal suppliedto the electrode 11 of the tube 6 serves totrigger the tube and cause continuous operation by virtue of the factthat the distributor .brush contacts now with the segment 5 whichcontinues until the distributor brush-again reaches the segment 5 afterwhich this operation is repeated, provided there isan incoming signal totrigger the tube 6. In the case of a signal of greater length, such as aMorse dash, the glow-discharge gap is immediately re-struck.

The sequence of switch cycles should conveniently not be chosen toorapid inasmuch as with increasing switching speed also the difficultiesinherent in synchronization will grow, and since, moreover, owing to therapid interruption of the transmitters, the side-bands that are radiatedoif also grow in size.

Another manner of carrying the basic idea of the invention into effectcomprises the employment of automatic or machine transmitters operatingwith perforated tapes for signal transmission. Inthis case it isfeasible to insuretimeconsecution or joining of the equi-wavetransmitters by the stepwise production of a certain number of signalsby causing the travel or conveyance of the perforated paper tape toproceed alternately in synchronous sections. The arrangements at thereceiving end, fundamentally speaking, remain the same as hereinbeforedescribed, though there is here no need for the accumulation of thesignals. Whererecorder reception is resorted to, the conveyance of thepaper is also conveniently caused by stages or intermittently. Whilethis method reduces the mean speed of telegraphy of each one of then-many lines to the nth part, this fact is mostly of little importancesofar as the field of application of this method is concerned seeingthat the combination of a plurality of lines of communication in onewave is primarily intended and useful for lines carrying usually lowloads for which, however, perfect working readiness is a primedesideratum.

For insuring and maintaining synchronism in rotation of the. constituentswitches comprised in the transmitter and receiver equipments and of theautomatic transmitters and inkers or other recording devices most of thesynchronizing methods known in the prior art may be adopted. Forinstance, tuning forks tuned to the same frequency. in conjunction withsynchronous motors could be employed. If necessary, correction of thephase of the synchronized parts may be produced at certain timeintervals in known manner by the aid of special impulses radiated of!from the transmitter or else by the telegraphic signals themselves. Forthe same object a combination of an electric contact-making pendulum anda stepping mechanism could be used.

The arrangement becomes particularly simple in nature when a duplexconnection is established in a manner as hereinbefore described inasmuchas in that case the transmitter and receiver switches could then beconstructionally combined at each end, or could at least be kept insynchronism by one and the same tuning fork. The method first describedabove involving a rotation or change-over of the different lines being'rapid comparatively with the length of the signals, however, is liableto cause difliculties in this case because of thefinite length of travelof the radio signals. If the time of transmission or travel from thesender to the receiver amounts to t seconds, it can be readily foundthat reception undisturbed by the sending part of the station will befeasible at both ends only if the number of switching periods k persecond is equal to:

l T2t2t2t Hence, this difilculty can be obviated by the suitable choiceof the switch frequency as shown,

It s etc;

When short waves are used, the spreading or echo effects peculiarthereto and occasioned-by extended or multiplied received signals isliable to result in disturbances of equi-wave operation in so far assignals of one line of communication, after the change-over of thetelegraphic channels, are apt to be picked up by the next receiver setin the rotation of connections. This source of trouble may be overcomeif the rotation or sequence of the n-many channels or connections is notchosen unduly fast, by making the different switch segments less than360mm, so that after each switch or signal period there is provided ablank orperiod free from a signal. This scheme would appear of advantagealso for the reason that this eliminates slight discrepancies insynchronization.

In what precedes the assumption had been made that the synchronouscircuit changes or connections are established by mechanical, moreparticularly revolving switch mechanism. Of

munication is to be used for picture telegraphy comprising the use ofdrums, it will not be necessary to stop the picture drums both at thesender and at the receiver during the transmission intervals or spaces.If the duration of the differ-- ent transmission periods is vmade equalto the time required by the picture drums for completing a revolution,'then, for n-many equi-wave lines it is sufl'icient to reduce the axialshift of all picture drums to the nth part of the pitch governed by thewidth of the picture elements.

Hence, each picture will thus be transmitted inside an n-times longtime, but the fineness of the screen or subdivision of the picture willbe unimpaired. The sending and receiving switches should in this schemebe constructionally combined-with the picture apparatus in order thattheir switching rhythm should bear. a suitable relationto the rotationof the picture drums. In this way separate synchronization for theswitch mechanism would be dispensed with.

Having now described our invention, what we claim and desire to secureby Letters Patent is the following:

1. In a multiplex communication system, means for transmitting aplurality of messages, means for dividing the time period oftransmission between each of said messages into a plurality ofsequentially recurring periods each of a duration no greater than theduration of the brieiest signal to be transmitted, means for receivingsignal corresponding to each of the independent messages, and means foraccumulating the separate message signals for a time period greater thanthe recurrences of the same message, and means for recording theaccumulated message signals.

3. In a multiplex communication system, means for transmitting aplurality of messages, means for dividing the time period oftransmission between each of said messages into a plurality ofsequentially recurring periods each of a duration no greater than theduration of the briefest signal to be transmitted, means for receivingsignals corresponding to each of the independent messages, and a glowdischarge relay for accumulating the separate message signals for a timeperiod greater than the time division in periods between successiverecurrences of the same message.

4. In a multiplex communication system, the method of receiving aplurality of signals transmitted over a single carrier which includesthe steps of transmitting a plurality of messages,

dividing the time period of transmission for each of said messages intoa plurality of sequentially recurring periods each of a duration nogreater than the time duration of the briefest signal to be transmitted,reeciving all of the signals, and accumulating the separate signals forrecording for a time period greater than the time division in theperiodsbetween successive recurrences of the same message signal.

5. In a multiplex communication system, the method of receiving aplurality of signals transmitted over a single carrier which includesthe steps of transmitting a plurality of messages,

dividing the time period of transmission for each of said messages intoa plurality of sequentially recurring periods each of a duration nogreater than the time duration of the briefest signal to be transmitted,receiving all of the signals, accumulating the separate signals forrecording for a time period greater than the time-division in theperiods between successive recurrences of the same message signal,and'recording each sequentially recurring accumulated signal.

6. In a multiplex communication system, means for transmitting aplurality of messages, means for dividing the time period oftransmission between each of said messages into a plurality ofsequentially recurring periods each of a duration no greater than theduration of the briefest si nal to be transmitted, means for receivingsignals corresponding to each of the independent messages, signalrecording means for reproducing the signals, said means being normallyslow in responding and rapid in releasing, and a glowdischarge relay foraccumulating the separate message signals for a time period greater thanthe time division in periods between successive recurrences of the samemessage so as to actuate the signal recording means.

FRITZ SCHRGTER. WALDEMAR ILBERG.

